1. Field of the invention
The present invention relates to a device for inserting optical fibers into helical grooves of a ring travelling axially in a cabling line to obtain an optical fiber cable.
On the upstream side of the inserting device, the fibers are drawn from pay-out spools turning freely or braked, on a support plate which rotates around the strand and converge following cone generating lines towards the device. The rotational speed of the support plate is slaved at the apparent rotational speed of the grooves in the travelling ring, so that the fibers are correctly inserted in the grooves irrespective of pitch variation of the grooves as a result of manufacturing the ring by extrusion. On the downstream side of the device, the ring enters at least one taping unit to close the grooves containing the optical fibers by applying a protective sheath around the ring.
2. Description of the Prior Art
According to the prior art described in French patents Nos. 2,388,931, 2,418,940, 2,500,174, U.K. Pat. Nos. 2,022,644 and 2,121,209, and U.S. Pat. No. 4,635,430, an optical fiber inserting device comprises a fiber-guide support rotating coaxially to the ring and offering either ducts or grooves or capillary tubes or metal fiber-guides housed in conduits or grooves of the support, which converge along generating lines of a cone coaxial with the ring and act as fiber-guides to guide respectively the fibers drawn following the generating lines from the spools on the support plate towards the ring grooves.
As for the support plate, rotation of the fiber-guides support depends upon variations of the pitch of the ring grooves. Rotational coupling between the ring and the fiber-guide support is generally obtained either by pointed or bevelled downstream ends of the fiber-guides recessed in the ring grooves or by at least one locating and driving finger projecting from within a bore of the fiber-guide support and mating with a specific helical groove formed in the ring, or a groove intended to accommodate one optical fiber.
The use of such a fiber-guide support as described in U.S. Pat. No. 4,635,430 requires in practice some means for laying the optical fibers in the grooves since, as seen in cross-section to the ring, the downstream ends of the fiber-guides fill the ring grooves, and the fiber-guides insert the fibers exactly at the periphery of the ring, at a relatively large distance from the bottom of the grooves. The laying means consists of a rotation-stationary quill arranged on the downstream side of the fiber-guides support, in front of the downstream ends of the fiber-guides in the ring grooves, and traversed coaxially and freely by the ring.
The known inserting devices have many disadvantages:
the fiber-guide support and more particularly the fiber-guides, are complex members requiring careful manufacture to a high degree of precision and are in consequence expensive;
The fiber-guides which are thin and elongate by comparison with the exceedingly small diameter of the optical fibers which they guide, are firstly subject to obstruction by dirt and dust, and secondly are liable to bend or in some cases to break or crack, especially when the cabling line is started up and the ring is initially drawn manually, or when there are variations in the groove pitch and also in the groove section during operation of the line, as the result of the coupling between the ring and the fiber-guide support through the downstream ends of the fiber-guides;
although a fixed quill is occasionally installed to lay the fibers as they are inserted into the grooves, the fibers "float" in the ring grooves as they leave the inserting device so that some fibers tend to remain at the outer periphery of the ring and so become wedged or broken during the later ring raping, drawing and twisting operations.